Re: Root cause of the issue that HVM guest boots slowly with pvops dom0

["Yang, Xiaowei" <xiaowei.yang@intel.com>]

Keir Fraser wrote:
> On 22/01/2010 08:07, "Yang, Xiaowei" <xiaowei.yang@intel.com> wrote:
> 
>>> How does the attached patch work for you? It ought to get you the same
>>> speedup as your hack.
>> The speed should be almost the same, regardless of twice memcpy.
> 
> Did you actually try it out and confirm that?

Yes, I tried it out. And there are no obvious speed difference comparing your 
patch (my comment 1 included) and the hack.

> 
>> Some comments to your trial patch:
>> 1.
>> diff -r 6b61ef936e69 tools/libxc/xc_private.c
>> --- a/tools/libxc/xc_private.c Fri Jan 22 14:50:30 2010 +0800
>> +++ b/tools/libxc/xc_private.c Fri Jan 22 15:32:48 2010 +0800
> 
> Yes, missed that all-important bit!
> 
>> 2. _xc_clean_hcall_buf needs a more careful NULL pointer check.
> 
> Not really: free() accepts NULL. But I suppose it would be clearer to put
> the free(hcall_buf) inside the if(hcall_buf) block.
> 
>> 3. It does modification to 5 out of 73 hypercalls invoking mlock. Other
>> problem 
>> hypercalls could turn out to be the bottleneck later?:)
> 
> The point of a new interface was to be able to do the callers incrementally.
> A bit of care is needed on each one, and most are not and probably never
> will be bottlenecks.

Agree. Anyway when we meet other pvops performance issue later, let's go back 
and have a check at this aspect.

Thanks,
xiaowei